Non-aqueous electrolyte secondary cell

ABSTRACT

A non-aqueous electrolyte secondary battery using composite particles for its negative electrode. In the composite particles, nucleus particles including at least one element selected from tin, silicon, and zinc as their constituent element are entirely or partly covered with a solid solution or inter-metallic compound of said constituent element and at least one element selected from groups consisting of Group 2 elements, transition elements, and Group 12, Group 13, and Group 14 elements in the Periodic Table except for the constituent element of the nucleus particles and carbon. Further, the present invention is characterized in that the NMR signals of the lithium intercalated in the composite particles appear within the range of −10 to 40 ppm with respect to lithium chloride and at least one signal appears within the range of −10 to 4 ppm.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national phase of PCT/JP00/02502 filed on Apr. 8,2000 which is a continuation-in-part of U.S. patent application Ser. No.09/090,484, filed Jun. 3, 1998, now U.S. Pat. No. 6,090,505, issued Jul.18, 2000.

FIELD OF THE INVENTION

The present invention relates to non-aqueous electrolyte secondarybatteries, particularly to non-aqueous electrolyte secondary batteries(hereinafter referred to as “secondary batteries”) with high energydensity and improved electrochemical characteristics, such ascharge/discharge capacity and cycle life, that are provided by theimproved negative electrode material and non-aqueous electrolyte.

BACKGROUND OF THE INVENTION

High electromotive force and high energy density are featured by lithiumsecondary batteries recently used for such mobile communicationsequipment as personal digital assistants and mobile electronic apparatus, main power supply for the mobile electronic gears, small domesticpower storage devices, and motor bicycles, electric vehicles, and hybridcars using motors as their driving sources.

Lithium ion secondary batteries using organic electrolytic solutions,carbon materials as their negative electrode active materials, andlithium-containing composite oxides as their positive electrode activematerials have higher energy density and more excellent low-temperaturecharacteristics than secondary batteries using aqueous solutions.Moreover, without using lithium metals for their negative electrodes,lithium ion secondary batteries also have excellent cycle stability andsafety, thus rapidly becoming commercially practical. Lithium polymerbatteries using electrolytes like macromolecular (polymer) gelcontaining organic electrolytic solutions are also being developed as anew battery family of thin and light type.

When a lithium metal with high capacity is used as negative electrodematerial, dendrite-like deposition is formed on the negative electrodeduring charging. During repeated charge and discharge operations, thedendrite may penetrate the separator or polymer gel electrolyte, reachthe positive electrode side and thus cause internal short circuits.Having a large specific surface area and thus high reactivity, thelithium deposition reacts with the solvent, becomes inactive, anddecreases the charge/discharge efficiency. This phenomenon increases theinternal resistance of the battery and produces particles isolated fromelectronic conduction network, thus decreasing the charge/dischargeefficiency of the battery. For these reasons, lithium secondarybatteries using lithium metals as their negative electrode materialshave problems of having low reliability and poor cycle lifecharacteristics.

At present, lithium secondary batteries use, for their negativeelectrodes, carbon materials capable of intercalating andde-intercalating lithium ions, and have become commercially available.Generally, since metal lithium does not deposit on a carbon negativeelectrode, it does not cause the problem of internal short circuitsresulting from the production of dendrite. However, the theoreticalcapacity of graphite, one of carbon materials now in use, is 372 mAh/g,which is so small as one-tenth the theoretical capacity of pure Limetal.

As other negative electrode materials, metallic and non-metallic pureelements that form compounds with lithium are known. For example, thecomposition formula of a compound of tin (Sn), silicon (Si), or zinc(Zn) containing largest amount of lithium is expressed by Li₂₂Sn₅,Li₂₂Si₅, or LiZn, respectively. Within this composition range,generally, no metallic lithium deposits; therefore, there is no problemof internal short circuits caused by the formation of dendrite. Theelectrochemical capacities between these compounds and each of the pureelements are 993 mAh/g, 4,199 mAh/g, and 410 mAh/g, respectively, all ofwhich are larger than that of graphite.

Other compounds for negative electrode materials proposed include anonferrous metal silicide consisting of transition elements disclosed inJapanese Patent Laid-Open Publication No. H07-240201, and a negativeelectrode material consisting of an inter-metallic compound containingat least one element selected from Group 4B elements, P, and Sb andhaving a crystal structure of one of CaF₂, ZnS, or AlLiSi type disclosedin Japanese Patent Laid-Open Publication No.H09-63651.

However, each of the aforementioned negative electrode materials withhigh capacity has the following problems.

Generally, the negative electrode materials of metallic and non-metallicpure elements that form compounds with lithium exhibit poorercharge/discharge cycle characteristics than carbon negative electrodematerials. This is probably because the negative electrode materialsbreak by their volumetric expansion and shrinkage.

Meanwhile, unlike the aforementioned pure elements, a negative electrodematerial that consists of a nonferrous metal silicide consisting oftransition elements and an inter-metallic compound that contains atleast one element selected from Group 4B elements, P, and Sb and has acrystal structure of one of CaF₂, ZnS, or AlLiSi type are proposed asnegative electrode materials with improved cycle life characteristics inJapanese Patent Laid-Open Publication No.H07-240201 and No.H09-63651,respectively. In Japanese Patent laid-Open Publication No.H10-208741,the range of nuclear magnetic resonance (hereinafter abbreviated as NMR)signals of lithium intercalated in the negative electrode material isproposed.

In the battery using the nonferrous metal silicide consisting oftransition elements as the negative electrode material disclosed inJapanese Patent Laid-Open Publication No.H07-240201, while the dischargecapacities at the first, fiftieth and hundredth cycles shown in itsexamples and a comparative example indicate that its charge/dischargecycle characteristics have been more improved than those of the lithiummetal negative electrode material , the discharge capacities have onlyincreased by about 12% at maximum compared with that of the naturalgraphite negative electrode material.

For the material disclosed in Japanese Patent Laid-Open PublicationNo.H09-63651, its examples and comparative examples show that it hasmore improved charge/discharge cycle characteristics than the negativeelectrode material of Li—Pb alloy and has higher discharge capacity thangraphite. However, the battery considerably decreases its dischargecapacity at 10 to 20 charge/discharge cycles and even with Mg₂Sn that isconsidered best, its capacity decreases to 70% of its initial capacityafter about 20 cycles. For this reason, this material is inferior incharge/discharge characteristics.

For the material disclosed in Japanese Patent Laid-Open Publication No.H10-208741, NMR signals of the lithium intercalated in various alloysappear within the range of 5 to 40 ppm. By using this material, anelectrode material with high energy density and excellent cycle life isproposed. However, as for the cycle life of the battery using thiselectrode material, its capacity decreases to 70% of its maximum after372 cycles even when LiCoO2 is used for its positive electrode.

The present invention addresses the aforementioned problems conventionalbatteries have.

SUMMARY OF THE INVENTION

The negative electrode of the battery of the present invention ischaracterized by the use of composite particles. In the compositeparticles, nucleus particles containing at least one element selectedfrom tin , silicon, and zinc as their primary constituent element arecovered with a solid solution or inter-metallic compound of the elementsconstituting the nucleus particles and at least one element selectedfrom groups consisting of Group 2 elements, transition elements, andGroup 12, Group 13, and Group 14 elements in the Periodic Table exceptfor carbon and constituent element of the nucleus particles. Further,the negative electrode of the battery of the present invention ischaracterized in that NMR signals of the lithium intercalated in thenegative electrode material appear within the range of −10 to 40 ppmwith respect to lithium chloride as a reference and at least one NMRsignal appears within the range of −10 to 4 ppm. In addition , thenegative electrode of the battery of the present invention ischaracterized in that the above NMR signals with respect to lithiumchloride as a reference appear within the range of −10 to 4 ppm and −10to 20 ppm and the NMR signal intensity appearing within the range of −10to 4 ppm is 1 to 10 times as large as those appearing within the rangeof 10 to 20 ppm.

With the aforementioned structure, non-aqueous electrolyte secondarybatteries that address the problems of conventional batteries and havehigher energy density and more excellent cycle characteristics can beprovided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal section of a cylindrical battery of the presentinvention.

PREFERRED EMBODIMENTS OF THE INVENTION

The battery of the present invention has positive and negativeelectrodes capable of intercalating and de-intercalating lithium, anon-aqueous electrolytic solution and a separator or a solidelectrolyte.

The negative electrode material of the present invention uses compositeparticles in which nucleus particles comprising solid phase A areentirely or partly covered with solid phase B.

Solid phase A includes of at least one element selected from tin,silicon, and zinc.

Solid phase B includes a solid solution or an inter-metallic compound ofat least one element selected from tin, silicon, and zinc and the otherelements. The other elements constituting solid phase B comprise atleast one element selected from groups consisting of Group 2 elements,transition elements, and Group 12, Group 13, and Group 14 elements inthe periodic table except for the above constituent element and carbon.

In the following, the above negative electrode material of the presentinvention is referred to as “composite particles”. By using the abovecomposite particles as negative electrode material, solid phase Binhibits the expansion and shrinkage caused by charge and discharge ofsolid phase A, and thus the negative electrode material with excellentcharge/discharge cycle characteristics can be obtained.

In the negative electrode material of the present invention, solid phaseA is considered to mainly contribute to increase charge/dischargecapacity because it contains at least one element selected from tin,silicon, and zinc that have high capacity. Solid phase B entirely orpartly covering the nucleus particles consisting of solid phase Acontributes to the improvement in charge/discharge cyclecharacteristics. The amount of lithium contained in solid phase B isgenerally smaller than that contained in the pure metal, solid solution,or inter-metallic compound.

In other words, the negative electrode material used in the presentinvention is made of nucleus particles comprising at least one elementselected from tin, silicon, and zinc that provide high capacity, and asolid solution or inter-metallic compound that is unlikely to pulverizeand covers the nucleus particles. The solid solution or inter-metalliccompound of the covering layer can restrain a change in the crystalstructure of the nucleus particles, i.e. a large volumetric change, thusinhibiting the pulverization of the nucleus particles.

When the negative electrode materials react with lithium, lithium existsin the composite particles with covalent bonds or as ions. The NMRsignals of covalent bonded ⁷Li appear within the range of 10 to 20 ppm.The site in which covalent bonded lithium exists is hereinafter referredto as “X site”. The NMR signals of ⁷Li ions appear within the range of−10 and 40 ppm. The site in which lithium ion exists is hereinafterreferred to as “Y site”.

The Y site partly includes the signals related to irreversible factors.Such signals are generally found for negative electrodes of carbonmaterials, and seldom found for those of the present invention.

As described above, when a large amount of reversible X and Y sites oflithium exist, high capacity and excellent cycle characteristics can beobtained. In other words, appearance of the NMR signals of ⁷Li withinthe range of −10 to 40 ppm and −10 to 4 ppm at the same time in acharged state show the existence of both X and Y sites. It was foundthat high capacity and excellent cycle characteristics can be attainedin such a state.

Moreover, it was found that higher capacity and more excellent cyclecharacteristics can be attained when the strength of signals appearingwithin the range of −10 to 4 ppm indicating the existence of the Y siteare 1 to 10 times as large as those of the signals appearing within therange of 10 to 20 ppm indicating the existence of the X site.

As described above, the present invention discriminates how lithium hasbeen intercalated in the negative electrode material, i.e. as ions orcovalent bonded, and determines the existence ratio using the NMRsignals of ⁷Li to provide the material with high capacity and excellentcycle characteristics.

In other words, in order to exhibit high capacity and excellent cyclecharacteristics, the NMR signals of ⁷Li of the negative electrodematerial should appear within the range of −10 to 40 ppm and −10 to 4ppm in a charged state.

The NMR signals of ⁷Li appearing within the range of −10 to 40 ppm showsthe existence of ⁷Li ions and covalent bonded ⁷Li mixed. The NMR signalsof ⁷Li appearing within the range of −10 and 4 ppm shows the existenceof lithium ions that provides high capacity. Moreover, when the signalsappearing within the range of −10 to 4 ppm that indicates the existenceof lithium ions are 1 to 10 times as large as those appearing within therange of 10 to, 20 ppm that indicates the existence of covalent bondedlithium, much higher capacity can be attained.

The positive and negative electrodes used for the present invention aremade by applying the surface of a current collector with a layer of anelectrode mixture. The mixture contains positive electrode activematerials or the above negative electrode materials capable ofelectrochemically and reversibly intercalating and de-intercalatinglithium ions together with a conductive material, binder, and the like.

Next, producing methods of composite particles used as the negativeelectrode materials are described.

One method of producing composite particles includes:

quenching and solidifying the melt containing each element constitutingthe composite particles in the composition ratios , using dryatomization, wet atomization, roll quenching, rotating electrode method,and other methods; and

heat-treating the solidified material at a temperature lower than thesolid line temperature of the solid solution or inter-metallic compound.The solid line temperature is determined by the composition ratio.

Quenching and solidifying the melt allows particles of solid phase A todeposit as the nucleus of the particles and solid phase B to deposit soas to entirely or partly cover the particles of solid phase A.Thereafter, heat treatment can improve the homogeneity of each of thesolid phases A and B. Even when the above heat treatment is notperformed, composite particles appropriate for the present invention canbe obtained. Another cooling method can be used on condition that it cansufficiently cool the melt at a high speed.

Another production method is forming an layer comprising elementsrequired for forming solid phase B over the surfaces of the powder ofsolid phase A, and heat-treating it at a temperature lower than thesolid line temperature. This heat treatment allows component elements insolid phase A to diffuse toward the layer and to form solid phase B as acovering layer. The layer is formed using plating, mechanical alloying,or other method. The mechanical alloying method does not require heattreatment. Any method capable of forming the layer can be used.

Conductive materials for the negative electrodes can be any electronicconductive materials. Examples of such materials include: graphitematerials including natural graphite (scale-like graphite), artificialgraphite, and expanded graphite; carbon black materials such asacetylene black, high-structure carbon black typified by Ketzen black,channel black, furnace black, lamp black and thermal black; conductivefibers such as carbon fibers and metal fibers; metal powders such ascopper and nickel; and organic conductive materials such aspolyphenylene derivatives. These materials can be used independently orin combination. Among these conductive materials, artificial graphite,acetylene black, and carbon fibers are especially preferable.

The amount of conductive materials to be added is not specificallydefined; however, 1 to 50 wt %, especially 1 to 30 wt %, of the negativeelectrode material is preferable. Having electronic conductivity initself, the negative electrode material of the present invention(composite particles) can work as a battery electrode material withoutany additional conductive materials. Thus, more composite particles canbe included in the electrode by the amount of conductive materials.

For binders for the negative electrodes, both thermoplastic resin andthermosetting resin can be used. Preferable binders for the presentinvention include the following materials: polyethylene, polypropylene,polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF),styrene-butadiene rubber, a tetrafluoroethylene-hexafluoropropylenecopolymer (FEP), a tetrafluoroethylene-perfluoroalkyl vinyl ethercopolymer (PFA), a vinylidene fluoride-hexafluoropropylene copolymer, avinylidene fluoride-chlorotrifluoroethylene copolymer, aethylene-tetrafluoroethylene copolymer (ETFE resin), polychlorotrifluoroethylene (PCTFE), a vinylidenefluoride-pentafluoropropylene copolymer, a propylene-tetrafluoroethylenecopolymer, a ethylene-chlorotrifluoroethylene copolymer (ECTFE), avinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, avinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylenecopolymer, an ethylene-acrylic acid copolymer or its Na+ ioncrosslinking body, an ethylene-methacrylic acid copolymer or its Na+ ioncrosslinking body, an ethylene-methyl acrylate copolymer or its Na+ ioncrosslinking body, and an ethylene-methyl methacrylate copolymer or itsNa+ ion crosslinking body. These materials can be used independently orin combination. Preferable materials among these materials arestyrene-butadiene rubber , polyvinylidene fluoride, an ethylene-acrylicacid copolymer or its Na+ ion crosslinking body, an ethylene-methacrylicacid copolymer or its Na+ ion crosslinking body, an ethylene-methylacrylate copolymer or its Na+ ion crosslinking body, and anethylene-methyl methacrylate copolymer or its Na+ ion crosslinking body.

For current collectors for the negative electrodes, any electronicconductive material can be used on condition that it does not chemicallychange in the battery constructed. Examples of such materials includestainless steel, nickel, copper, titanium, carbon, and conductive resinas well as copper or stainless steel surface-treated with carbon,nickel, or titanium. Among these, copper and copper alloys areespecially preferable. These materials can also be used after theirsurfaces have been oxidized. Desirably, the current collector issurface-treated to have roughened surface. The shapes of the currentcollector include a film, sheet, net, punched sheet, lath, porous body,foam, and formed and grouped fibers as well as a foil. The thickness isnot specifically defined; however, collectors 1 to 500 μm thick areused.

As positive electrode active materials, compounds containing lithium orcontaining no lithium can be used. Such compounds include Li_(x)CoO₂,Li_(x)NiO₂, Li_(x)MnO₂, Li_(x)Co_(y)Ni_(1-y)O₂,Li_(x)Co_(y)M_(1-y)O_(z), Li_(x)Ni_(1-y)M_(y)O_(z), Li_(x)Mn₂O₄, andLi_(x)Mn_(2-y)M_(y)O₄ (M is at least one of Na, Mg, Sc, Y, Mn, Fe, Co,Ni, Cu, Zn, Al, Cr, Pb, Sb and B, where x=0-1.2, Y=0-0.9, z=2.0-2.3).The above value x is the value before charging and discharging; thus itchanges along with charging and discharging. Other usable positiveelectrode materials include transition metal chalcogenides, a vanadiumoxide and its lithium compounds, a niobium oxide and its lithiumcompounds, a conjugate polymer using organic conductive materials, andseveral phase compounds. It is also possible to use a plurality ofdifferent positive electrode materials in combination. The averagediameter of particles of the positive electrode active materials is notspecifically defined; however, desirably it is 1-30 μm.

Conductive materials for the positive electrode can be any electronicconductive material on condition that it does not chemically changewithin the range of charge and discharge electric potentials of thepositive electrode materials in use. Examples of such materials include: graphite materials including natural graphite (scale-like graphite)and artificial graphite; carbon black materials such as acetylene black,high-structure carbon black typified by Ketzen black, channel black,furnace black, lamp black and thermal black; conductive fibers such ascarbon fibers and metal fibers; metal powders such as fluorinated carbonand aluminum; conductive whiskers such as a zinc oxide and potassiumtitanate; conductive metal oxides such as a titanium oxide; and organicconductive materials such as polyphenylene derivatives. These materialscan be used independently or in combination. Among these conductivematerials, artificial graphite and acetylene black are especiallypreferable. The amount of conductive materials to be added is notspecifically defined; however, 1 to 50 wt %, especially 1 to 30 wt %, ofthe positive electrode material is preferable. For carbon and graphite,2 to 15 wt % is especially preferable.

For binders for the positive electrodes, both thermoplastic andthermosetting resins can be used. The aforementioned binders for thenegative electrodes can preferably be used, and more preferablematerials are PVDF and PTFE.

For current collectors for the positive electrodes, any electronicconductive material can be used on condition that it does not chemicallychange within electric potentials in the range of charge and dischargeof the positive electrode material in use. For example, theaforementioned current collectors for the negative electrode canpreferably be used. The thickness is not specifically defined; however,collectors 1 to 500 μm thick are used.

The electrode mixtures for the negative and positive electrode plates,can include filler, dispersant, ion conductor, pressure intensifier andother various additives as well as a conductive material and binder. Asthe filler, any fibrous material that does not chemically change in theconstructed battery can be used. Generally, olefinic polymers such aspolypropylene and polyethylene and such fibers as glass fibers andcarbon fibers are used. The amount of the filler to be added is notspecifically defined; however, 0 to 30 wt % of the electrode mixture ispreferable.

Preferably, the negative and positive electrodes are structured so thatat least the surface made of the negative electrode mixture is oppositethe surface made of the positive electrode mixture.

The non-aqueous electrolytes used for the present invention are composedof non-aqueous solvents and lithium salts dissolved in the solvents.Examples of such non-aqueous solvents include: cyclic carbonates such asethylene carbonate (EC), propylene carbonate (PC), butylene carbonate(BC), and vinylene carbonate (VC); acyclic carbonates such as dimethylcarbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC),and dipropyl carbonate (DPC); aliphatic carboxylates such as methylformate, methyl acetate, methyl propionate, and ethyl propionate;γ-lactones such as γ-butyrolactone; acyclic ethers such as 1,2-dimethoxyethane (DME), 1,2-diethoxy ethane (DEE), and ethoxy methoxy ethane(EME); cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran; and non-protonic organic solvents such as dimethylsulfoxide, 1,3-dioxolane, formamide, acetamide, dimethylformamide,dioxolane, acetonitrile, propylnitrile, nitromethane, ethyl monoglime,triester of phosphoric acid , trimethoxy methane, dioxolane derivatives,sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone,3-methyl-2-oxazolidinone, propylene carbonate derivatives,tetrahydrofuran derivatives, ethyl ether, 1,3-propane saltane, anisole,dimethyl sulfoxide and N-methylpyrolidon. These solvents are usedindependently or as a mixture of one, two or more solvents. Among these,mixtures of cyclic carbonate and acyclic carbonate, or mixtures ofcyclic carbonate, acyclic carbonate and aliphatic carboxylate areespecially preferable.

Lithium salts dissolved into the above solvents include LiClO₄, LiBF₄,LiPF₆, LiAlCl₄, LiSbF₆, LiSCN, LiCl, LiCF₃SO₃, LiCF₃CO₂, Li (CF₃SO₂)₂,LiAsF₆, LiN(CF₃SO₂)₂, LiB₁₀Cl₁₀, lithium salt of lower aliphaticcarboxylic acid, LiCl, LiBr, LiI, chloroboron lithium, 4-phenil boricacid, and an imide group. These lithium salts can be dissolved in theabove non-aqueous solvents individually or in combination of two or morelithium salts to use as an electrolytic solution. It is especiallypreferable to include LiPF₆ in the electrolytic solution.

Especially preferable non-aqueous electrolytes of the present inventionincludes at least EC and EMC, and as a supporting salt, LiPF₆. Theamount of the electrolyte to be added to the battery is not specificallydefined. Considering the amount of the positive and negative electrodematerials and the size of the battery, the required amount is used. Theamount of the supporting electrolytes against the non-aqueous solventsis not specifically defined; however, 0.2 to 2 mol/l is preferable, andespecially 0.5 to 1.5 mol/l is more preferable.

Besides the electrolytic solutions, the following solid electrolytes canalso be used. The solid electrolytes are classified into inorganic andorganic ones.

Well known inorganic solid electrolytes are lithium nitrides, lithiumhalides, and lithium oxides, and the like. Among them, Li₄SiO₄,Li₄SiO₄—LiI—LiOH, xLi₃PO₄—(1−x)Li₄SiO₄, Li₂SiS₃, Li₃PO₄—Li₂S—SiS₂ andphosphorus sulfide compounds can be used effectively.

As the organic solid electrolytes, polymer materials such aspolyethylene oxides, polypropylene oxides, polyphosphazene,polyaziridine, polyethylene sulfides, polyvinyl alcohol, polyvinylidenefluorides, polyhexafluoropropylene and their derivatives, mixtures andcomplexes can effectively be used.

Moreover, it is effective to add other compounds to the electrolyticsolution in order to improve discharge and charge/dischargecharacteristics. Such compounds include triethyl phosphite,triethanolamine, cyclic ethers, ethylene diamine, n-glime, pyridine,triamide hexaphosphate, nitrobenzene derivatives, crown ethers,quaternary ammonium salts, and ethylene glycol dialkyl ether.

As separators, insulating micro-porous thin film having large ionpermeability and predetermined mechanical strength is used. Desirably,these separators have functions of closing their pores and increasingresistance above predetermined temperatures. In terms of resistance toorganic solvents and hydrophobic properties, olefinic polymers such aspolypropylene and polyethylene are used independently or in combination,or sheets and woven or non-woven fabrics made of glass fibers, and thelike, are used. Desirably, the micro-porous separator has pores of adiameter that does not allow the positive or negative electrodematerial, binder, and conductive material liberated from the electrodesheets to pass. For example, pores 0.01 to 1 μm in diameter arepreferable. Generally, separators 10 to 300 μm thick are used. Theporosity of the separator is determined according to the permeability ofelectrons and ions, materials, and thickness. Generally, a porosity of30 to 80% is desirable.

A battery with integrated porous separator and positive and negativeelectrodes can be constructed. The integrated positive and negativeelectrode mixtures contain a polymer material that absorbs and holds anorganic electrolytic solution composed of a solvent and a lithium saltdissolved in the solvent. The separator is composed of a polymerabsorbing and holding the organic electrolytic solution. In this case,any polymer material capable of absorbing and holding the organicelectrolytic solution can be used. Especially, a vinylidenefluoride—hexafluoropropylene copolymer is preferable.

The battery can be of any shape including a coin, button, sheet,lamination, cylinder, flat, square, and a large type used for anelectric vehicle.

The materials used for the batteries of the present invention arehereinafter described in detail. However, the present invention is notlimited to these examples.

The positive and negative electrodes used for the batteries of thepresent invention are made of current collectors coated with themixtures. The mixtures are essentially include positive electrode activematerial and negative electrode material capable of electrochemicallyand reversibly intercalating and de-intercalating lithium ions, andconductive materials and binder.

Production of Composite Particles

Table 1 shows the composition of solid phases A and B of the compositeparticles (single element, inter-metallic compound, and solid solution)used for the examples of the present invention, ratios of the elementsat preparation, fusing temperatures, and solid line temperatures.

Powder or a block of each element constituting composite particles wasput into a crucible in the composition ratio shown in Table 1. Thematerial was fused at a temperature shown in Table 1 and quenched usingthe roll quenching method and solidified to obtain a solidifiedmaterial. Sequentially, the solidified material was heat-treated in aninert atmosphere at a temperature about 10 to 50° C. lower than thesolid line temperature shown in Table 1 for 20 hours. The heat-treatedmaterial was pulverized with a ball mill and classified with a sieve toobtain composite particles 45 μm or smaller in size. Electron microscopeobservations verified that these particles were made of particles ofsolid phase A entirely or partly covered with particles of solid phaseB.

The structure of the batteries of the present invention is describedwith reference to specific examples of a cylindrical battery.

EXAMPLE 1

FIG. 1 shows a longitudinal section of the cylindrical battery of thepresent invention. Positive electrode plate 5 and negative electrodeplate 6 are spirally wound via separator 6 and housed in battery case 1.Positive electrode lead 5 a is led out from the positive electrode plate5 and connected to sealing plate 2. Negative electrode lead 6 a is ledout from negative electrode plate 6 and connected to the bottom ofbattery case 1.

Metals and alloys having electronic conductivity and resistance toorganic electrolytic solutions can be used for the battery case and leadplate. For example, metals such as iron, nickel, titanium, chromium,molybdenum, copper, and aluminum, and their alloys are used. Stainlesssteel plates or processed Al—Mn alloy plates are especially preferablematerials for the battery case, aluminum for the positive electrodelead, and nickel for the negative electrode lead. For the battery case,various kinds of engineering plastics and those in combination withmetals can be used to reduce its weight.

Insulating rings 8 are provided on the top and bottom of groupedelectrode plates 4, respectively. The sealing plate can be used as asafety valve. Conventionally known various safety elements can beinstalled other than the safety valve. Such safety elements include afuse, bimetal, and PTC device functioning as an overcurrent protectiondevice. Other than the safety valve, notching the battery case, crackingthe gasket, cracking the sealing plate, or breaking connection with thelead can also be used to prevent an increase in internal pressure of thebattery case. A protection circuit capable of protecting from overchargeor overdischarge can be incorporated in a battery charger or providedindependently. In addition, a system in which an increase in theinternal pressure of the battery case breaks the current can beincorporated to eliminate overcharge. In this case, compounds capable ofincreasing the internal pressure can be contained in the electrodemixtures or electrolytes. Such compounds include carbonates such asLi₂CO₃, LiHCO₃, Na₂CO₃, NaHCO₃, CaCO3, and MgCO₃.

For welding the cap, battery case, sheet and lead, well-known methods(e.g. electric welding using direct or alternating current, laserwelding, and ultrasonic welding) can be used. As the sealing materialsfor sealing the openings, conventionally known compounds and mixtures,such as asphalt, can be used.

Negative electrode plate 6 was made by:

mixing 20 wt % of carbon powder, 5 wt % of PVDF and 75 wt % of compositeparticles synthesized under the above conditions;

dispersing the mixture in dehydrated N-methyl pyrrolidinone to prepare aslurry;

coating the negative electrode current collector made of a copper foilwith the slurry; and

drying and then rolling it.

Positive electrode plate 5 was made by:

mixing 10 wt % of carbon powder, 5 wt % of PVDF and 85 wt % of lithiumcobaltate powder;

dispersing the mixture in dehydrated N-methylpyrrolidinone to prepare aslurry;

coating the positive electrode current collector made of a copper foilwith the slurry; and

drying and then rolling it.

An electrolytic solution containing 1.5 mol/l of LiPF₆ dissolved in amixed solvent of EC and EMC in a volumetric ratio of EC:EMC=1:1 wasused.

Thus, the batteries were made using the materials shown in Table 1 fortheir negative electrodes. The cylindrical batteries produced are 18 mmin diameter and 65 mm in height.

Comparative Example 1

A battery using graphite for its negative electrode was produced in thesame manner as Example 1 for comparison.

After these batteries were charged at a constant current of 100 mA, theywere discharged at a constant current of 100 mA to 2.0 V. Suchcharge/discharge cycles were repeated in an oven at a constanttemperature of 20° C. The charge/discharge cycles were repeated up to400 times and the ratio of the discharge capacity at the 400th cycle tothe initial discharge capacity was shown as a capacity retention rate inTable 2.

In addition, NMR measurement was performed on the ⁷Li of the negativeelectrode materials in a charged state and the NMR signals of theintercalated lithium were measured with respect to the lithium chlorideas a reference. Several NMR signals appeared within the range of −10 to40 ppm. FIG. 2 shows the positions at which the signals appeared and thesignal intensity ratio of the NMR signals appearing within the range of−10 to 4 ppm to those appearing within the range of 10 to 20 ppm. Due tovariations from lot to lot, the same material exhibited different signalpositions and intensities. The NMR measuring conditions of the ⁷Li areas follows:

Instrument: INOVA 400 (VARIAN Co.)

Temperature: room temperature

Measured nuclear: ⁷Li

Revolution of the samples: 10 kHz

Reference Material: LiCl 1M

Table 2 shows the followings about batteries A to S using materials A toS as negative electrode materials.

Even when the NMR signals of ⁷Li intercalated in the negative electrodematerials appear within the range of −10 to 40 ppm,

(1) in the case where no signals appear within the range of −10 to 4 ppmand

(2) in the case where all the signals appear in the magnetic field lowerthan 4 ppm,

the capacity retention rates after 400 cycles are high; however, theinitial capacities and the capacities after 400 cycles are lower thanthose of battery T using the graphite negative electrode.

In the case where the signals appear between the magnetic fields lowerthan 5 ppm and higher than −10 ppm, the initial capacities are large butthe capacity retention rates after 400 cycles are small and thedischarge capacities after 400 cycles are smaller than that of batteryT.

Meanwhile , when the signals appear within the range of −10 to 40 ppmand at least one signal appears within the range of −10 to 4 ppm, theinitial capacities are larger than that of battery T and the capacityretention rates after 400 cycles are 70% or higher and the capacitiesafter the cycles are larger than that of battery T.

When the signal strength of the signals appearing within the range of−10 to 4 ppm indicating the ⁷Li mainly in the ionic state is 1 to 10times as large as the signal strength of the signals appearing withinthe range of 10 to 20 ppm indicating the ⁷Li mainly covalent bonded, thecapacities after 400 cycles are the largest.

As mentioned above, when the NMR signals of lithium intercalated in thenegative electrode materials appear within the range of −10 to 40 ppmwith respect to lithium chloride as a reference and at least one NMRsignal appears within the range of −10 to 4 ppm, a secondary batterywith high capacity and excellent cycle characteristics can be obtained.Moreover, when the NMR signals of the lithium intercalated in thenegative electrode materials appearing within the range of −10 to 4 ppmare 1 to 10 times as large as those appearing within the range of 10 to20 ppm, a secondary battery with higher capacity and more excellentcycle characteristics can be obtained.

Regarding the elements constituting negative electrode materials, whensolid phase A is made of tin, Mg selected from Group 2 elements, Fe andMo from transition elements, Zn and Cd from Group 12 elements, In fromGroup 13 elements, and Pb from Group 14 elements are used. However,using other elements in each Group could provide similar results. Solidphase A may include any element other than tin, including a trace amountof such elements as O, C, N, S, Ca, Mg, Al, Fe, W, V, Ti, Cu, Cr, Co,and P.

Regarding the elements constituting negative electrode materials, whensolid phase A is made of silicon, Mg selected from Group 2 elements, Coand Ni from transition elements, Zn from Group 12 elements, Al fromGroup 13 elements, and Sn from Group 14 elements are used. However,using other elements in each Group can provide similar results.

In addition, when solid phase A is made of zinc, Mg selected from Group2 elements, Cu and V from transition elements, Cd from Group 12elements, Al from Group 13 elements, and Ge from Group 14 elements areused. However, using other elements in each Group can provide similarresults.

The composition ratios of the elements constituting the negativeelectrode materials are not specifically defined. Any composition can beused on condition that the elements provide two phases so that one phase(solid phase A) essentially consists of tin, silicon, and zinc, and theother phase (solid phase B) entirely or partly covers the surface ofsolid phase A. Solid phase A may contain any element except eachconstituent element, for example, a trace amount of such elements as O,C, N, S, Ca, Mg, Al, Fe, W. V, Ti, Cu, Cr, Co, and P.

As described above, a non-aqueous electrolyte secondary battery having,higher capacity and more excellent cycle characteristics thanconventional ones using carbon materials for their negative electrodescan be obtained, when the battery uses aforementioned compositeparticles composed of nucleus particles of solid phase A and solid phaseB entirely or partly covering the solid phase A, and NMR signals of thelithium intercalated in the negative electrode material appear withinthe range of−10 to 40 ppm with respect to lithium chloride as areference and at least one signal appears within the range of −10 to 4ppm. Moreover, a non-aqueous electrolyte secondary battery with highercapacity and more excellent cycle characteristics than conventional onesusing carbon materials for their negative electrodes can be obtainedwhen the NMR signals of the lithium intercalated in the negativeelectrode material appearing within the range of −10 to 4 ppm withrespect to lithium chloride as a reference is 1 to 10 times as large asthose appearing within the range of 10 to 20 ppm.

INDUSTRIAL APPLICABILITY

The secondary battery using the composite particles for the negativeelectrode in accordance with the present invention has higher energydensity and more effects on the improvement in charge/discharge cyclelife characteristics than the conventional batteries using carbonmaterials for their negative electrodes. For this reason, the secondarybattery of the present invention can be used for personal digitalassistants, mobile electronic equipment, small domestic power storagedevices, motor bicycles, electric vehicles, hybrid cars, and the like,thus providing great industrial effects. The uses of the secondarybattery of the present invention are not limited to those describedabove, and can be used for any application requiring a secondarybattery.

TABLE 1 Solid Fusing line Negative Solid Solid temper- temper-Composition electrode phase phase ature ature ratio material A B (° C.)(° C.) (atomic %) Material A Sn Mg₂Sn 770 204 Sn:Mg = 50:50 Material BSn FeSn₂ 1540 513 Sn:Fe = 70:30 Material C Sn MoSn₂ 1200 800 Sn:Mo =70:30 Material D Sn Solid solution 420 199 Sn:Zn = 90:10 of Zn and SnMaterial E Sn Solid solution 232 133 Sn:Cd = 95:5 of Cd and Sn MaterialF Sn Solid solution 235 224 Sn:In = 98:2 of In and Sn Material G SnSolid solution 232 183 Sn:Pb = 80:20 of Sn and Pb Material H Si Mg₂Si1415 946 Si:Mg = 70:30 Material I Si CoSi₂ 1495 1256 Si:Co = 85:15Material J Si NiSi₂ 1415 993 Si:Ni = 69:31 Material K Si Solid solution1415 420 Si:Zn = 50:50 of Si and Zn Material L Si Solid solution 1415577 Si:Al = 40:60 of Si and Al Material Si Solid solution 1415 232 Si:Sn= 50:50 M of Si and Sn Material N Zn Mg₂Zn₁₁ 650 364 Zn:Mg = 92.9:7.8Material O Zn Solid solution 1085 425 Zn:Cu = 97:3 of Zn and Cu MaterialP Zn VZn₁₁ 700 420 Zn:V = 94:6 Material Q Zn Solid solution 420 266Zn:Cd = 50:50 of Zn and Cd Material R Zn Solid solution 661 381 Zn:Al =90:10 of Zn and Al Material S Zn Solid solution 938 394 Zn:Ge = 97:3 ofZn and Ge

TABLE 2 NMR Initial Discharge Charging signal Strength dischargecapacity after Capacity Electrode voltage positions ratio* capacity400th cycle retention rate Battery material (V) (ppm) (times) (mAH)(mAH) (%) A Material A 4.0 8, 13 0.5 1081  864 80 4.05 4, 13 0.8 13321038 78 4.1 −4, 13 1 1566 1205 77 4.15 −6, 13 10 1633 1208 74 4.18 −10,13 12 1659 1161 70 4.2 −12, 13 15 1766  512 29 B Material B 4.0 7, 130.4 1077  872 81 4.05 4, 13 0.9 1473 1148 78 4.1 −2, 13 1 1789 1359 764.15 −5, 13 10 1849 1386 75 4.18 −10, 13 12 1855 1298 70 4.2 −13, 13 151898  284 15 C Material C 4.0 6, 13 0.5 1067  853 80 4.05 3, 13 0.7 16001248 78 4.1 −5, 13 2 1825 1350 74 4.15 −6, 13 10 1834 1338 73 4.18 −10,13 12 1847 1292 70 4.2 −11, 13 14 1859 390 21 D Material D 4.0 6, 13 0.51047  827 79 4.05 4, 13 0.8 1578 1230 78 4.1 −4, 13 1 1829 1371 75 4.15−4, 13 8 1839 1360 74 4.18 −10, 13 12 1852 1296 70 4.2 −12, 13 15 1877 356 19 E Material E 4.0 8, 13 0.5 1001  800 80 4.05 4, 13 0.8 1613 125878 4.1 −4, 13 1 1861 1414 76 4.15 −5, 13 10 1874 1386 74 4.18 −10, 13 111876 1313 70 4.2 −11, 13 12 1899  338 21 F Material F 4.0 8, 13 0.5 1073 879 82 4.05 4, 13 0.8 1623 1265 78 4.1 −4, 13 1 1846 1420 77 4.15 −6,13 10 1852 1389 75 4.18 −9, 13 11 1861 1302 70 4.2 −12, 13 12 1888  33918 G Material G 4.0 6, 13 0.5 1054  832 79 4.05 4, 13 0.8 1572 1227 784.1 −3, 13 1.5 1833 1411 77 4.15 −4, 13 10 1848 1404 76 4.18 −10, 13 121855 1317 71 4.2 −11, 13 15 1899  474 25 H Material H 4.0 6, 13 0.5 1091 872 80 4.05 3, 13 0.7 1702 1327 78 4.1 −4, 13 1 1931 1467 76 4.15 −5,13 8 1945 1458 75 4.18 −10, 13 13 1958 1370 70 4.2 −12, 13 15 1968  41321 I Material I 4.0 8, 13 0.5 1059  857 81 4.05 4, 13 0.8 1677 1308 784.1 −4, 13 2.1 1911 1433 75 4.15 −6, 13 10 1924 1404 73 4.18 −10, 13 121935 1354 70 4.2 −12, 13 15 1940  465 24 J Material J 4.0 7, 13 0.5 1069 855 80 4.05 3, 13 0.65 1546 1221 79 4.1 −4, 13 1 1926 1502 78 4.15 −5,13 10 1973 1499 76 4.18 −10, 13 12 1974 1381 70 4.2 −12, 13 15 1985  47624 K Material K 4.0 7, 13 0.5 1069  855 80 4.05 3, 13 0.8 1578 1230 784.1 −4, 13 1 1918 1476 77 4.15 −4, 13 10 1932 1449 75 4.18 −10, 13 121944 1360 70 4.2 −12, 13 13 1969  433 22 L Material L 4.0 8, 13 0.5 1066 863 81 4.05 4, 13 0.8 1769 1379 78 4.1 −4, 13 1 1921 1459 76 4.15 −5,13 8 1943 1457 75 4.18 −9, 13 11 1966 1395 71 4.2 −11, 13 15 1989  57629 M Material M 4.0 8, 13 0.5 1021  816 80 4.05 2, 13 0.7 1682 1328 794.1 −3, 13 1 1902 1483 78 4.15 −6, 13 10 1923 1461 76 4.18 −10, 13 111945 1361 70 4.2 −12, 13 15 1981  455 23 N Material N 4.0 8, 13 0.5 1039 851 82 4.05 4, 13 0.8 1508 1176 78 4.1 −4, 13 1 1764 1358 77 4.15 −5,13 9 1789 1341 75 4.18 −10, 13 12 1809 1266 70 4.2 −12, 13 13 1817  36320 O Material O 4.0 8, 13 0.5 1039  808 80 4.05 4, 13 0.8 1510 1177 784.1 −4, 13 1 1751 1348 77 4.15 −6, 13 10 1810 1357 75 4.18 −10, 13 111815 1270 70 4.2 −12, 13 12 1828  530 29 P Material P 4.0 8, 13 0.5 1002 801 80 4.05 3, 13 0.8 1474 1149 78 4.1 −4, 13 1.5 1692 1302 77 4.15 −7,13 10 1755 1316 75 4.18 −10, 13 12 1799 1259 70 4.2 −12, 13 15 1805  41523 Q Material Q 4.0 6, 13 0.5 1099  868 79 4.05 4, 13 0.8 1508 1176 784.1 −4, 13 1 1719 1323 77 4.15 −5, 13 10 1755 1333 76 4.18 −10, 13 121800 1260 70 4.2 −12, 13 15 1805  541 30 R Material R 4.0 8, 13 0.5 1092 862 79 4.05 3, 13 0.8 1445 1141 78 4.1 −4, 13 1.2 1754 1350 77 4.15 −6,13 10 1800 1368 76 4.18 −10, 13 12 1805 1281 71 4.2 −12, 13 14 1810  32518 S Material S 4.0 8, 13 0.5 1098  878 80 4.05 4, 13 0.7 1455 1134 784.1 −4, 13 1 1710 1316 77 4.15 −8, 13 10 1745 1308 75 4.18 −10, 13 121795 1256 70 4.2 −12, 13 15 1809  434 24 T Graphite 4.2 — — 1510  906 60

What is claimed is:
 1. A non-aqueous electrolyte secondary batteryhaving a non-aqueous electrolyte, separator, and positive and negativeelectrodes capable of intercalating and de-intercalating lithium, saidnegative electrode including composite particles including at least oneelement selected from tin, silicon, and zinc as a constituent elementthereof and at least one of: (a) a solid solution of said constituentelement and at least one element selected from groups consisting ofGroup 2 elements, transition elements, Group 12, Group 13, and Group 14elements in a Periodic Table except for said constituent element andcarbon; and (b) an inter-metallic compound of said constituent elementand at least one element selected from groups consisting of Group 2elements, transition elements, Group 12, Group 13, and Group 14 elementsin the Periodic Table except for said constituent element and carbon,covering said particles entirely or partly, said electrode materialincludes an amount of lithium which produces a plurality of NMR signalsbetween −10 to 40 ppm with at least one signal between −10 to 4 withrespect to a reference of lithium chloride.
 2. A non-aqueous electrolytesecondary battery of claim 1 wherein a signal strength of said NMRsignals appearing within the range of −10 to 4 ppm are 1 to 10 times ofa NMR signal strength appearing within the range of 10 to 20 ppm.